The Arabidopsis Na super(+)/H super(+) Exchanger AtNHX1 Catalyzes Low Affinity Na super(+) and K super(+) Transport in Reconstituted Liposomes

In saline environments, plants accumulate Na super(+) in vacuoles through the activity of tonoplast Na super(+)/H super(+) antiporters. The first gene for a putative plant vacuolar Na super(+)/H super(+) antiporter, AtNHX1, was isolated from Arabidopsis and shown to increase plant tolerance to NaCl....

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Bibliographic Details
Published in:The Journal of biological chemistry 2002-01, Vol.277 (4), p.2413-2418
Main Authors: Venema, K, Quintero, F J, Pardo, J M, Donaire, J P
Format: Article
Language:English
Subjects:
Arabidopsis thaliana
AtNHX1 gene
AtNHX1 protein
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Summary:In saline environments, plants accumulate Na super(+) in vacuoles through the activity of tonoplast Na super(+)/H super(+) antiporters. The first gene for a putative plant vacuolar Na super(+)/H super(+) antiporter, AtNHX1, was isolated from Arabidopsis and shown to increase plant tolerance to NaCl. However, AtNHX1 mRNA was up-regulated by Na super(+) or K super(+) salts in plants and substituted for the homologous protein of yeast to restore tolerance to several toxic cations. To study the ion selectivity of the AtNHX1 protein, we have purified a histidine-tagged version of the protein from yeast microsomes by Ni super(2+) affinity chromatography, reconstituted the protein into lipid vesicles, and measured cation-dependent H super(+) exchange with the fluorescent pH indicator pyranine. The protein catalyzed Na super(+) and K super(+) transport with similar affinity in the presence of a pH gradient. Li super(+) and Cs super(+) ions were also transported with lower affinity. Ion exchange by AtNHX1 was inhibited 70% by the amiloride analog ethylisopropyl-amiloride. Our data indicate a role for intracellular antiporters in organelle pH control and osmoregulation.
ISSN:0021-9258